This application incorporates by reference of Taiwan application Serial No. 090119364, filed Aug. 9, 2001.
1. Field of the Invention
The invention relates in general to a display apparatus, and more particularly to a display apparatus with a time domain multiplex driving circuit.
2. Description of the Related Art
Featuring the favorable properties of thinness, lightness and generating low radiation, Liquid Crystal Display (LCDs) have been widely used in the world.
FIG. 1 shows a circuit diagram illustrating a conventional LCD panel. The display panel includes a plurality of pixels (P). The pixels are arranged in the form of a matrix on the display panel. The display panel includes an active matrix driving circuit for driving the pixels. The active matrix driving circuit includes a plurality of scan lines (S), a plurality of data lines (D), and a plurality of switching devices. The switching devices are set in the pixels for selectively transmitting the corresponding data signals to the pixels. The switching device can be a thin film transistor (TFT) such as an n-type field effect transistor (n-FET) or a p-type field effect transistor (p-FET). In FIG. 1, the switching device of each pixel includes a thin film transistor. The thin film transistor in each pixel includes a gate electrode, a first source/drain electrode, and a second source/drain electrode. The gate electrode of the thin film transistor is coupled to the corresponding scan line and the first source/drain electrode is coupled to the corresponding data line. Take the pixel P(m,n) for example. The pixel P(m,n) includes a thin film transistor M1. The gate electrode of the thin film transistor M1 is coupled to the scan line Sm, and the first source/drain electrode of the thin film transistor M1 is coupled to the data line Dn. Each scan line is perpendicular to each data line. Each pixel in the same pixel row is coupled to the same scan line and each pixel in the same pixel column is coupled to the same data line, as shown in FIG. 1.
FIG. 2 shows the configuration of a conventional active matrix liquid crystal display. The conventional active matrix liquid crystal display includes a display panel 202, an X board 214, and a Y board 212. The display panel 202 includes the pixels and the active matrix driving circuit, as shown in FIG. 1. The X board 214 is coupled to a plurality of scan drivers 206 set in the tape carrier packages 210. Each scan driver 206 is coupled to the X board 214 and the corresponding scan lines respectively. The Y board 212 is coupled to a plurality of data drivers 204 set in the tape carrier packages (TCP) 208. Each data driver 204 is coupled to the Y board 212 and the corresponding data lines respectively. The X board 214 and the scan drivers 206 are used for enabling the corresponding scan lines through inputting a scan signal into the scan line. When the scan line is enabled, each pixel in the pixel row coupled to the scan line can be turned ON. The Y board 212 and the data drivers 204 are used for inputting the data signals to the corresponding pixels through the corresponding data lines when the pixels are turned ON.
The conventional active matrix liquid crystal display has the following disadvantages. First, a large number of data lines are needed. For example, an active matrix display panel has a resolution of 1024xc3x97768, that is, the active matrix display panel having 1024 pixel columns and each pixel column having 1024xc3x973=3072 pixels. Therefore, the active matrix display panel must include 3072 data lines. The number of the data lines is large. Besides, since there are so many data lines are needed, the pitch between the adjacent data lines must be small. Second, each data line is coupled to the corresponding data driver through the outer lead of the tape carrier package. It is difficult and elaborate to connect all data lines to the corresponding outer leads of the tape carrier packages. Third, the aperture ratio of the display panel will be decreased since the number of the data lines is so large.
FIG. 3 shows the diagram of the conventional time domain multiplex driving circuit. In the conventional time domain multiplex driving circuit, every two adjacent pixels in the same pixel row are coupled to the same data line. These two pixels are set on the left and right sides of the data line respectively. The pixel set on the left side of the data line is called the left pixel (LP) and the pixel set on the right side of the data line is called the right pixel (RP). The switching devices of the pixels LP and RP are different. Take the pixels LP(m,n) and RP(m,n) as an example. These two pixels are coupled to both the same scan line Sm and the same data line Dn. The pixel LP(m,n) is set on the left side of the data line Dn and the pixel RP(m,n) is set on the right side of the data line Dn, as shown in FIG. 3. The switching device of the pixel RP(m,n) includes a thin film transistor M2. The gate electrode of the thin film transistor M2 is coupled to the scan line Sm and the first source/drain electrode of the thin film transistor M2 is coupled to the data line Dn. The switching device of the pixel LP(m,n) is different from that of the pixel RP(m,n). The switching device of the pixel LP(m,n) includes two thin film transistors M11 and M12. The gate electrode of the thin film transistor M11 is coupled to the scan line Sm+1 and the first source/drain electrode of the thin film transistor M11 is coupled to the data line Dn. The gate electrode of the thin film transistor M12 is coupled to the scan line Sm and the first source/drain electrode of the thin film transistor M12 is coupled to the second source/drain electrode of the thin film transistor M11, as shown in FIG. 3.
FIG. 4 shows the timing chart of the scan signals of the scan lines Sm, Sm+1, and Sm+2 and the ON and OFF status of the corresponding pixels LP(m,n), RP(m,n), LP(m+1,n), and RP(m+1,n) shown in FIG. 3. The method for driving display panel with the above-described time domain multiplex driving circuit is called a time domain multiplex driving method. When the time domain multiplex driving method is executed, each pixel row is driven in turn by the time domain multiplex driving circuit. The time domain multiplex driving method includes two scanning procedures. The first scanning procedure is to selectively turn on the left pixels of the pixel row by turning on two corresponding TFTs of each of the left pixels and then feeding the corresponding data signals into the respective left pixels. The second scanning procedure is to selectively turn on the right pixels of the pixel row by turning on one corresponding TFT of each right pixel and then feeding the corresponding data signals into the respective right pixels.
Take pixels LP(m,n) and RP(m,n) shown in FIG. 3 as an example. In the time period T1, the scan line Sm and Sm+1 are enabled. The thin film transistor M11 and M12 can be turned ON and a data signal can be inputted to the corresponding pixel LP(m,n) through the TFTs M11 and M12. In the time period T2, only the scan line Sm is enabled. The thin film transistor M2 can be turned ON and a data signal can be inputted to the corresponding pixel RP(m,n) through the TFT M2.
In the time domain multiplex driving circuit, the above-described disadvantages of the conventional active matrix driving circuit can be improved. If the resolution of the display panel is 1024xc3x97768, for example, every two adjacent pixels in the same pixel row are coupled to one corresponding data line of the time domain multiplex driving circuit, and thus only 3072/2=1536 data lines are needed.
However, the conventional time domain multiplex driving circuit disclosed above has the following disadvantages. First, an equivalent resistor Ro is produced between the first source/drain electrode and the second source/drain electrode when the thin film transistor is turned on. The driving time needed to input the data signal into the corresponding pixel may be affected by the equivalent resistor Ro of the thin film transistor. The larger the resistance of the resistor Ro is, the more the driving time is needed to drive the pixels. In FIG. 1, the switching device of the pixel P(m,n) includes only one thin film transistor M1. Thus, the equivalent resistor of the pixel P(m,n) shown in FIG. 1 is Ro. In FIG. 3, the pixel LP(m,n) includes two thin film transistors M11 and M12. The data signal must pass through both of the thin film transistors M11 and M12 to get into the pixel LP(m,n). Therefore, the equivalent resistor of the pixel LP(m,n) shown in FIG. 3 is 2Ro, two times that of the pixel P(m,n) shown in FIG. 1. When the pixels are driven by the time domain multiplex driving circuit, the driving time needed to input all data signals into the corresponding pixels must be longer.
Second, an equivalent capacitor between the gate electrode and the second source/drain electrode is produced when the thin film transistor is turned ON. The output voltage will be lower than the input voltage of the thin film transistor and the luminance of the pixel may be decreased because of the equivalent capacitor. This effect caused by the equivalent capacitor is called the feed-through effect. The larger the capacitance of the equivalent capacitor is, the larger the difference between the output voltage and the input voltage of the thin film transistor is. Take the pixels LP(m,n) and RP(m,n) shown in FIG. 3 as an example. The switching device of the pixel RP(m,n) includes only one thin film transistor M2 and the switching device of the pixel LP(m,n) includes two thin film transistors M11 and M12. The data signal inputted to the pixel RP(m,n) only through the thin film transistors M2 but the data signal inputted to the pixel LP(m,n) through two thin film transistors, M11 and M12. Therefore, the equivalent capacitor of LP(m,n) is much larger than that of RP(m,n). During driving the pixels by the time domain multiplex driving circuit, the luminance of the pixel LP(m,n) will be smaller than that of the pixel RP(m,n) when the data signals inputted to the pixel LP(m,n) and RP(m,n) are of the same magnitude. The display performance of the liquid crystal display would thus be degraded.
Third, the luminance of a display panel whose pixels are arranged according to the structure shown in FIG. 3 would be non-uniform when identical data signals are applied to all pixels of the display. This phenomenon is called odd-even line. For the display panel according to FIG. 3, each pixel of the odd (or even) pixel columns includes two TFTs and each pixel of the even (or odd) pixel columns includes one TFT, so that the equivalent capacitances of the adjacent pixel columns are different, thus resulting in the non-uniformity of luminance. The display quality of the liquid crystal display may be degraded because of the odd-even line problem.
According to the foregoing descriptions, the conventional time domain multiplex driving circuit has the following disadvantages. First, the driving time needed to input the data signals into the corresponding pixels must be longer. Second, the display performance may be degraded. Third, the odd-even line problem may happen.
It is therefore an objective of the present invention to provide a display apparatus with a new time domain multiplex driving circuit for driving the pixels of the display apparatus so as to achieve the objectives: First, the number of the data lines can be decreased. Second, it takes less driving time to input the data signals into the corresponding pixels. Third, the display performance of the display panel cannot be affected.
According to the objectives of the present invention, it is provided a display apparatus comprising a first, a second, and a third in parallel scan lines, a first data line perpendicular to the scan lines, a first pixel coupled to the first data line, the first scan line and the second scan line respectively, a second pixel coupled to the first data line and the first scan line respectively, a third pixel coupled to the first data line and the second scan line respectively, and a fourth pixel coupled to the first data line, the second scan line and the third scan line respectively. The first pixel and the third pixel are on the same side of the first data line and the second pixel and the fourth pixel are on the other side of the first data line.
Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.